Area forecast discussion
National Weather Service Medford or
1100 am PDT sun may 19 2013
Discussion...very light isolated showers remain north of the Umpqua
Divide this morning will continue to diminish as the ridge continue
to build into the region. Offshore flow intensifies and spreads
east...and warming ensues.
Previous discussion...although the bulk of the precipitation
associated with the yesterday's cold front has moved out of the
area...some isolated light shows will linger through the morning.
Most of this precipitation is the result of marine layer clouds
banked along the coast...and upslope along the foothills of the
Cascades north of the Umpqua Divide. Measurable rainfall from these
showers will be hard to find...and all activity should end by this
afternoon.
Meanwhile...large scale middle level ridging will build into the West
Coast from the eastern Pacific...and the thermal trough to our
south will begin to intensify. The results will be what we would
normally expect...dry...warm conditions and clear skies...as well
as gusty winds along the coast and along the ridgelines west of
the Cascades and south of the Umpqua Divide. The Chetco effect
will also be in play...resulting in well above normal temperatures
for portions of the southwest Oregon coast both today and on
Monday. How warm the area gets Monday will depend greatly on the
timing of an expected shift in the flow late Monday morning or early
in the afternoon. The later the shift...the warmer the area could
get. Current thinking is that more normal temperatures will make
their return along the coast of Curry County by middle afternoon.
Warm and dry conditions will be short lived...as the much
anticipated cut-off low finally begins to make its entrance into
the region Monday afternoon and evening. Models have been hitting
this system very hard for several days...depicting the low digging
south along the coast from the Gulf of Alaska late Monday into
Tuesday...and taking up residence over the Pacific northwest by
Tuesday evening. At this time in the evolution of the system...both
model
agreement and run to run consistency have suffered...mostly as a
result of the inability to resolve the behavior of a weak blocking
pattern upstream over central North America...and the potential
for kicker lows to move in across the North Pacific. What is
consistent is the presence of the low...and there is good
confidence that the low will remain over the region for the
duration of the forecast term. The result will be a wet and very
much cooler than normal forecast extending from middle week through
the Memorial Day weekend. The exact timing and amount of
precipitation will greatly depend on the timing of shortwaves
orbiting around the low...and the wobble of the low as this
occurs. Latest model guidance depicts the first wave of precipitation to
enter the area Tuesday night...and this will stay mostly confined
to the west side and Cascades. However...each subsequent wave will
push farther inland as moisture flow increases. Due to the
increase in confidence early in the event...have increased probability of precipitation and
coverage of precipitation through Wednesday night. Otherwise...have left
above climatology probability of precipitation in the forecast for the remainder of the extended
term.
Of other note during this event...snow levels will drop
considerably as the low digs in...and may reach below 3000 feet in
many places by Wednesday morning. This could potentially result in
measurable snowfall at many pass levels...and across much of the
east side. As mentioned above...near normal temperatures today
will warm to well above normal Monday...before dropping
drastically Tuesday and remaining well below normal for the
remainder of the forecast. High temperatures Wednesday and beyond
could drop to 20 degrees below normal...while nighttime lows could
even drop into the 30s in some west side valleys by Wednesday
night.
Those who may be traveling or participating in outdoor
activities this Holiday weekend...and agricultural interests at
higher elevations...should keep updated on the forecast...and take
the necessary precautions to prepare for the cold...wet...and
potentially snowy weather.
&&
Based on the 19/18z taf cycle.
Stratus with MVFR ceilings and mountain obscurations exist over
Coos County and the Umpqua this morning, spilling into northern
portions of Curry, much of Josephine, and northwestern Jackson
counties. Expect primary valley taf sites to become VFR late this
morning through early afternoon, but some partial mountain
obscurations are likely to linger over the western Umpqua basin
through the afternoon and into the evening. Overnight northeast to
east offshore flow is expected to prevent the formation of any
appreciable areas of low clouds or fog, so VFR conditions are
expected to prevail tonight through Monday morning. Btl
&&
Mfr watches/warnings/advisories...
or...none.
California...none.
Pacific coastal waters...Small Craft Advisory for winds from 11 am
this morning to 5 am
PDT Tuesday for pzz356.
Small Craft Advisory for hazardous seas from 11 am this morning
to 5 am PDT Tuesday for pzz356.
Small Craft Advisory for winds from 2 PM this afternoon to 11
PM
PDT Monday for pzz350-370.
Small Craft Advisory for hazardous seas from 2 PM this
afternoon
to 11 PM PDT Monday for pzz350-370.
Small Craft Advisory for winds until 2 PM PDT this afternoon
for
pzz376.
Hazardous seas warning from 2 PM this afternoon to 11 PM PDT
Monday for pzz376.
Gale Warning from 2 PM this afternoon to 11 PM PDT Monday for
pzz376.
Small Craft Advisory for hazardous seas until 2 PM PDT this
afternoon for pzz376.
$$
Sven/btl/bpn
